1. Field of the Invention
This invention relates to data sheets, and more particularly to a data sheet which is effective for the preservation of secrecy and the prevention of forgery and which makes it possible to miniaturize a reading device.
2. Description of the Prior Art
For example, a cash card employed in a bank or the like, and a credit card, railway ticket, admission ticket, bond, pari-mutuel ticket, etc. are designed such that characters, numerals, symbols, diagrams, patterns, etc. (in this specification, these shall be generically named "date," and a piece of paper, plastic film, cloth or the like on which the data are recorded shall be called a "data card") are entered in a predetermined blank form in advance. In use, the entered data are read by magnetic means, optical means or the like, and a predetermined decision is reached on the basis of the result.
A large number of types of data cards have hitherto been proposed.
The most typical data card is one in which data are recorded by a magnetic method. With this data card, desired data are encoded in a magnetic powder film applied on the front or rear surface of the card, while the reading is carried out by a magnetic method. The data card of this type is most widely employed for a credit card, a railway ticket, etc. Since, however, the information recorded magnetically can be seen with the eye or be transferred through proper means, the preservation of secrecy and the prevention of forgery are difficult. In addition, since the information registered magnetically can be easily erased by a magnetic field, the card is not adopted for uses requiring a high degree of reliability.
There has been proposed the card according to which data are entered on a card surface by the use of a fluorescent material in advance and are read with irradiating the card by ultraviolet rays so as to cause the fluorescent material to emit visible light (Japanese Utility Model Application Public-disclosure No. 117799/1974). However, a large-sized lamp is necessary for generating the ultraviolet rays. Moreover, the life of the mercury-arc lamp is problematic. Another drawback is that, since the visible light is given forth, the forgery or alteration is highly feared.
There has also been a data card of the system in which data are read by irradiating the surface of the card by light (visible light or infrared rays) and exploiting the difference of the light reflection factors of parts with data written down and the remaining part. Such a data card is extensively employed for the sorting of postal matter, etc. However, when a crease exists in the card or stains exist on the surface, the light reflection factor lowers and there is the likelihood of misconception. The preservation of secrecy is also questionable.
There has also been a data card in which holes piercing the card are provided, data being represented by the number or positions of the holes. It is disadvantageous, however, in that since the number or positions of the holes can be easily confirmed with the bodily eye, another person can readily counterfeit the card.
Many other data cards have been proposed, including one according to which a very small amount of radioactive substance is mixed in ink to be used for the recording of data so as to detect it by means of a Geiger counter (Official Gazette of Japanese Pat. No. 11380/1970), or one according to which a colored dielectric layer is provided, data being entered thereon by electrostatic recording (Official Gazette of Japanese Utility Model No. 16560/1975). None of them, however, is satisfactory, and a more excellent data card is strongly desired.